The present invention relates generally to apparatus and methods for detecting arc faults, and more specifically to arc fault detection apparatus and methods that are less susceptible to nuisance tripping.
U.S. patent application Ser. No. 10/937,487 filed Sep. 9, 2004 entitled APPARATUS AND METHOD FOR DETECTING ARC FAULTS (the '487 application) discloses an arc fault circuit interrupter (AFCI) device that can detect and distinguish between electrical arc faults and nuisance loads, and trip a circuit breaker to disconnect power to a load in the event electrical arcing has occurred. Electrical arc faults are generally non-periodic arcing events that may be caused by corroded, worn, aged, or otherwise damaged wiring or wire insulation, and/or faulty electrical connections. For example, electrical arcing can occur between the ends of a two wire conductor, between a conductor and ground, or between respective conductors connected to a load. In contrast, nuisance loads are generally associated with periodic electrical events that may be caused by triac-controlled dimmer circuits, switch-mode power supplies, appliance thermostat switching, drill current transitions, random line voltage spikes, or EMI bursts. Whereas electrical arcing may have the capability of igniting adjacent flammable material and therefore generally constitutes a fire hazard, nuisance loads typically do not create such hazardous conditions. Because the arc fault circuit interrupter disclosed in the '487 application can distinguish between many different types of electrical arc faults and nuisance loads, the AFCI device can disconnect power to a load upon detection of electrical arcing while being less susceptible to nuisance tripping.
Although the above-described arc fault circuit interrupter (AFCI) device has been successfully employed to detect and distinguish between electrical arcing and nuisance loads, there is a need for arc fault detection techniques that have increased reliability. For example, as described in the '487 application, the AFCI device is configured to generate an output that is a function of the differential of the power line current (di/dt). Because different types of electrical arcing typically produce different characteristic di/dt signatures, the AFCI device distinguishes between electrical arcing and nuisance loads based at least in part on characteristics of the differential current such as the di/dt level and the di/dt variation.
However, not only can different electrical arcing types produce different characteristic di/dt signatures, but they can also be associated with different characteristics in the line current waveform. For example, point contact electrical arcing can produce a number of sporadic high-level di/dt events with a large variation from cycle-to-cycle, while being associated with a line current waveform having a high peak-to-RMS current ratio. Further, series electrical arcing can produce an increased number of lower level di/dt events with reduced variation from cycle-to-cycle, while being associated with a line current waveform having a relatively low peak-to-RMS current ratio. Because the above-described AFCI device detects and distinguishes between electrical arcing and nuisance loads based on a consideration of the characteristic di/dt signature without considering the associated line current waveform characteristics, the device may detect what appears to be electrical arcing but instead is merely a nuisance load. This is because the line current waveform characteristics associated with the suspected electrical arc may not match the waveform characteristics normally associated with such arcing. As a result, the AFCI device may be prone to nuisance tripping.
It would therefore be desirable to have improved arc fault detection devices and techniques that avoid the drawbacks of conventional arc fault circuit interrupter (AFCI) devices and techniques.